package org.apache.maven.project;

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
import java.util.jar.JarFile;
import java.util.zip.ZipEntry;

import org.codehaus.plexus.util.IOUtil;
import org.codehaus.plexus.util.ReaderFactory;
import org.codehaus.plexus.util.xml.Xpp3Dom;
import org.codehaus.plexus.util.xml.Xpp3DomBuilder;
import org.codehaus.plexus.util.xml.pull.XmlPullParserException;

/**
 * Creates an extension descriptor from some XML stream.
 * 
 * @author Benjamin Bentmann
 */
class ExtensionDescriptorBuilder {

  private String getExtensionDescriptorLocation() {
    return "META-INF/maven/extension.xml";
  }

  /**
   * Extracts the extension descriptor (if any) from the specified JAR file.
   * 
   * @param extensionJar The JAR file or directory to extract the descriptor from, must not be
   *        {@code null}.
   * @return The extracted descriptor or {@code null} if no descriptor was found.
   * @throws IOException If the descriptor is present but could not be parsed.
   */
  public ExtensionDescriptor build(File extensionJar) throws IOException {
    ExtensionDescriptor extensionDescriptor = null;

    if (extensionJar.isFile()) {
      JarFile pluginJar = new JarFile(extensionJar, false);
      try {
        ZipEntry pluginDescriptorEntry = pluginJar.getEntry(getExtensionDescriptorLocation());

        if (pluginDescriptorEntry != null) {
          InputStream is = pluginJar.getInputStream(pluginDescriptorEntry);

          extensionDescriptor = build(is);
        }
      } finally {
        pluginJar.close();
      }
    } else {
      File pluginXml = new File(extensionJar, getExtensionDescriptorLocation());

      if (pluginXml.canRead()) {
        InputStream is = new BufferedInputStream(new FileInputStream(pluginXml));
        try {
          extensionDescriptor = build(is);
        } finally {
          IOUtil.close(is);
        }
      }
    }

    return extensionDescriptor;
  }

  ExtensionDescriptor build(InputStream is) throws IOException {
    ExtensionDescriptor extensionDescriptor = new ExtensionDescriptor();

    Xpp3Dom dom;
    try {
      dom = Xpp3DomBuilder.build(ReaderFactory.newXmlReader(is));
    } catch (XmlPullParserException e) {
      throw (IOException) new IOException(e.getMessage()).initCause(e);
    } finally {
      IOUtil.close(is);
    }

    if (!"extension".equals(dom.getName())) {
      throw new IOException("Unexpected root element \"" + dom.getName() + "\", expected \"extension\"");
    }

    extensionDescriptor.setExportedPackages(parseStrings(dom.getChild("exportedPackages")));

    extensionDescriptor.setExportedArtifacts(parseStrings(dom.getChild("exportedArtifacts")));

    return extensionDescriptor;
  }

  private List<String> parseStrings(Xpp3Dom dom) {
    List<String> strings = null;

    if (dom != null) {
      strings = new ArrayList<String>();

      for (Xpp3Dom child : dom.getChildren()) {
        String string = child.getValue();
        if (string != null) {
          string = string.trim();
          if (string.length() > 0) {
            strings.add(string);
          }
        }
      }
    }

    return strings;
  }

}
